1. Field of the Invention
This invention relates to a gas laser, which is in particular a ring resonator type gas laser. The present invention also relates to a gyro comprising a gas laser and a method of operating such a gyro. More particularly, the present invention relates to an optical gyro adapted to reduce the coupling loss generated when laser beams are incident upon a photodetector and the noise generated by the reflected beams reentering the laser from an external point of reflection as well as to a method of operating such an optical gyro.
2. Related Background Art
Mechanical gyros comprising a rotor and a vibrator as well as optical gyros adapted to detect the angular velocity of a moving object are known. Particularly, optical gyros are regarded as real innovation because they can start to operate instantaneously and provide a wide dynamic range. Optical gyros include ring resonator type laser gyros, optical fiber gyros and passive type ring resonator gyros, of which ring resonator type raser gyros comprising a gas laser were developed most early and have been used in aeronautic applications and other applications. Recently, small, high precision, ring resonator type laser gyros have been proposed and Japanese Patent Application Laid-Open No. 5-288556 described such a gyro.
However, known ring resonator type laser gyros are so designed that a laser beam propagating clockwise and another laser beam propagating counterclockwise are once emitted therefrom to the outside and received by a photodetector, which detects their optical beat and transforms it into an electric beat as a signal. This means that a coupling loss arises when the laser beams enter the photodetector. Additionally, known ring resonator type laser gyros need an optical isolator in order to avoid the noise generated by the beams reflected from an external point of reflection to the laser.
Particularly, since gas lasers are bulky and costly and consume driving electric power to a large extent, there is a strong demand for gyros comprising gas lasers that can be realized with a reduced number of components and hence at low cost and little power consumption.